The present invention relates to the specific field of turbomachines and it relates more particularly to the problem posed by assembling a metal end-wall of a combustion chamber in a turbomachine to the side walls of said chamber, when said side walls are made of a composite material of the ceramic matrix composite (CMC) type.
Conventionally, in a turbojet or a turboprop, the high pressure turbine, in particular its inlet nozzle (HPT nozzle), the injection system, the combustion chamber, and the casing (also called the shell) of said chamber are all made out of metal materials. However under certain particular conditions of use implementing particularly high combustion temperatures, a chamber made entirely of metal turns out to be completely unsuitable from a thermal point of view and it is necessary to make use of a chamber that is based on high temperature composite materials of the CMC type. However, since those materials are very costly and are unable to withstand strong mechanical stresses, they are generally restricted to being used for the composite chamber itself and more particularly to its axially-extending side walls only, with the high pressure turbine inlet nozzle, the injection system, and the casing then still being made more conventionally out of metal materials. Unfortunately, metals and composites have coefficients of thermal expansion that are very different. This gives rise to particularly awkward problems, specifically with connecting together the composite material side walls and the metal end-wall of the combustion chamber.
The present invention mitigates those drawbacks by proposing a mounting for the metal end-wall with the ability to accommodate the displacements induced by the different coefficients of expansion of the metal end-wall and of the composite side walls of the combustion chamber. An object of the invention is thus to provide a mounting that has good dynamic behavior and good sealing.
These objects are achieved by an annular combustion chamber including outer and inner axially-extending side walls of composite material and an end wall of metal material, said end wall being held in position on said outer and inner side walls by fixing means, wherein said fixing means pass through annular cavities that are designed to receive cylindrical end portions of said outer and inner side walls, and that are created between peripheral edges of said end wall and facing portions folded downstream, a determined amount of clearance J being provided between said peripheral edges and the facing faces of said outer and inner side walls in such a manner as to allow expansion to take place freely, in operation, in a radial direction between said end wall and said side walls.
With this system of fixing merely by means of bolts and sliding mounts, the expansion of the metal end-wall is accommodated without deteriorating the composite material walls.
The fixing means are constituted by a plurality of bolts, preferably captive-nut bolts.
The outer and inner side walls are advantageously provided with a plurality of holes designed to co-operate with said fixing means once said fixing means are mounted on said end wall.
In a preferred embodiment, the end wall can further comprise means to ensure sealing between said end wall and said side walls. The sealing means include a xe2x80x9cspring bladexe2x80x9d type circular gasket mounted in a circular groove of said metal end-wall and designed to bear on said facing side wall of the facing combustion chamber. In its downstream portion, said xe2x80x9cspring bladexe2x80x9d circular gasket preferably includes a rim designed to bear in toroidal manner on said facing side wall of the combustion chamber. Said circular sealing gasket should be divided into sectors, and held against said side wall by means of a resilient element fixed on said metal end-wall. The resilient element is constituted by a blade spring.
In an advantageous embodiment, the end wall can also integrate inner and outer caps of metal material which extend its peripheral edges upstream and provide better control over dynamic behavior.